LSO is generally recognized as the ideal scintillator for PET. It has high stopping power for 511 keV gamma rays, high light yield of over 30,000 photons/MeV, and rapid decay of 40 ns. It achieves high coincidence timing resolution and energy resolution. But single crystals of LSO are difficult and expensive to grow, reproducibility is poor, andthematerial is not readily available for general commercial use. In view of the many advantages of LSO, we have undertaken a new approach capable of producing LSO scintillators with properties rivaling those of the best crystals, yet remaining cost effective for fabrication in large quantities. This approach involves developing LSO detectors in the form of optical ceramics (OCs), rather than the single crystals that are now being used. Consolidation of powder into a fully dense ceramic provides many advantages over traditional single crystal growth, such as lower fabrication temperatures and simpler processing equipment. To overcome limits on transparency imposed by non-cubic crystal structure of LSO, our approach involves fabrication of ceramics with grain size limited to sub-micrometer region. Since the grain sizes now approach the wavelength of emitted light, scattering at grain boundaries is prevented and fully transparent material can be expected. The procedure has been completely confirmed in experiments on polycrystalline alumina, which is similarly anisotropic, and is being developed for optical window applications. It is the aim of this proposal to combine the two already developed technologies so as to produce LSO in the form of a fully transparent optical ceramic, which displays scintillation performance comparable to that of a single crystal. Construction of detector modules for PET imaging based on optically transparent ceramic LSO scintillators is also planned in the proposed effort. PUBLIC HEALTH RELEVANCE: The proposed research will investigate a promising detector technology which should have a major impact in health care, in particular, in the development of low cost detectors for in-vivo medical imaging. Other areas to which this research could be of benefit are: physics research, materials studies, homeland defense, and non-destructive testing.